• Journal of the Korean Recycled Construction Resources Institute
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• v.8 no.1
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• pp.88-96
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• 2020

In this study, the effect of cyclic wetting-drying on the self-healing of cementitious materials containing superabsorbent polymers (SAPs) were experimentally evaluated. In each cycle, cracked cement paste specimens containing various SAP dosages were exposed to wet conditions for 1 h, during which the capillary water absorption tests and water flow tests were conducted, and then exposed to dry conditions for 47 h. The capillary water absorption test results showed that the sorptivity values of the specimen without SAPs, SAP 0.5%, SAP 1.0%, and SAP 1.5% specimens were decreased by approximately 22.9%, 36.8%, 42.8%, and 46.3%, respectively, after 8 cycles. In addition, the water flow test results showed that the amount of water runoff through the cracks of all cracked specimens gradually decreased over wet/dry cycles, especially the reduction ratio of the amount of water runoff increased with increasing SAP dosage. Furthermore, the swelling behavior of SAPs in cracks by in gress water was con firmed via X-ray computed tomography (CT) analysis. These results indicate that the effective crack width can be reduced as SAPs absorb water and swell, while the water absorbed in SAPs can be released to crack surfaces under dry conditions, further promoting healing product formation. This study demon strates that the in corporation of SAPs can in crease the water tightness of cracks, thereby improving the self-healing efficiency of cementitious materials.

• Journal of the Korea institute for structural maintenance and inspection
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• v.23 no.7
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• pp.1-8
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• 2019

The primary purposes of this study are to understand a fundamental effects of electro-deposition on reinforcing steel in saturated Ca(OH)2 electrolyte, and evaluate the corrosion rates of rebars under cyclic 3wt.%NaCl immersion and dry corrosion environment. The three cement mortar specimens with cover thickness 5, 10 and 30mm, were prepared in the experiment. To monitor the corrosion rates of rebars in mortar, the three cement mortar specimens were exposed to 110 wet-drying cycles(8-hour-immersion in 3wt.%NaCl and 16-hour-drying in a room temperature) in the laboratory. During the wet-dry cycles, the polarization resistance, Rp, and solution resistance, Rs, were continuously measured. The instantaneous corrosion rates of rebars on the effect of electro-depositing with sat. Ca(OH)2 electrolyte were estimated from obtained R-1p and degrees of wetness were estimated from Rs values. From the experimental results, the corrosion rates of rebars were greatly accelerated by wet/dry cycles. During the mortars exposed to drying condition, the large increases in the corrosion rates were showed at all rebar surfaces in three mortar specimen, attributed from the accelerated reduction rates of dissolved oxygen in drying process. However, the corrosion rates on rebar surface electrochemically deposited with sat. Ca(OH)2 electrolyte showed the clear decreases, caused by calcium deposits in the porous rust layer.

• The Journal of Korean Academy of Prosthodontics
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• v.40 no.3
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• pp.287-295
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• 2002

Statement of Problem. Endodontically treated teeth frequently required posts and cores to provide retention and resistance form for crowns. In spite of excellent mechanical properties of metal post and core, its metallic color can be detected through all ceramic restorations occasionally. To solve esthetic problems of metal post and core zirconia post system has been introduced recently. Purpose. The purpose of this study was to examine the fracture strength and mode of resin root analogs restored with zirconia, gold and titanium posts with resin, ceramic and metal cores after cementation with metal crowns. Materials and methods. To avoid the morphological variations of natural teeth, 40 root analogs were fabricated with composite resin. Forty resin root analogs were randomly assigned to four groups according to post and core materials: Group A: cast gold post and core and complete cast crowns, as control. Group B: titanium posts (Parapost, Coltent/Whaledent Inc., NJ, USA) and composite resin cores. Group C: zirconia posts (Cosmopost, Ivoclar AG, Schaan/Liechtenstein) and composite resin cores Group D: zirconia posts and heat-pressed ceramic cores (IPS Empress Cosmo Ingots, Ivoclar AG) After thermocycling ($5^{\circ}C{\sim}55^{\circ}C$, 30 sec.), cyclic loading was applied at 3mm below the incisal edge on the palatal surfaces at an angle of 135 degree to the long axis (2Hz, 50N, 50000cycles). Fracture strength was measured by universal testing machine (Instron, High Wycombe, UK) and fracture pattern of restored resin root analogs was also evaluated. Results and conclusion. Within the limitations of this study following results were drawn. 1. Resin root analogs restored with zirconia posts and composite resins demonstrated lowest fracture strength among tested groups. 2. There was no significant difference in the fracture strength between zirconia posts and heat pressed glass ceramic cores and cast gold posts and cores 3. The fracture strength of resin root analogs restored with titanium posts and composite resin cores was lower than that of gold posts and cores. 4. The deep oblique fracture lines were dominantly observed in root analogs restored with cast gold post and core and zirconia post and heat-pressed ceramic core groups.

• Bulletin of the Korean Chemical Society
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• v.32 no.4
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• pp.1253-1257
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• 2011

The surface structures, adsorption conditions, and thermal desorption behaviors of cyclopentanethiol (CPT) self-assembled monolayers (SAMs) on Au(111) were investigated by scanning tunneling microscopy (STM), X-ray photoelectron spectroscopy (XPS), and thermal desorption spectroscopy (TDS). STM imaging revealed that although the adsorption of CPT on Au(111) at room temperature generates disordered SAMs, CPT molecules at $50^{\circ}C$ formed well-ordered SAMs with a $(2{\surd}3{\times}{\surd}5)R41^{\circ}$ packing structure. XPS measurements showed that CPT SAMs at room temperature were formed via chemical reactions between the sulfur atoms and gold surfaces. TDS measurements showed two dominant TD peaks for the decomposed fragments ($C_5H_9^+$, m/e = 69) generated via C-S bond cleavage and the parent molecular species ($C_5H_9SH^+$, m/e = 102) derived from a recombination of the chemisorbed thiolates and hydrogen atoms near 440 K. Interestingly, dimerization of sulfur atoms in n-alkanethiol SAMs usually occurs during thermal desorption and the same reaction did not happen for CPT SAMs, which may be due to the steric hindrance of cyclic rings of the CPT molecules. In this study, we demonstrated that the alicyclic ring of organic thiols strongly affected the surface structure and thermal desorption behavior of SAMs, thus providing a good method for controlling chemical and physical properties of organic thiol SAMs.

• Korean Chemical Engineering Research
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• v.56 no.3
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• pp.303-308
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• 2018

Silicon/Carbon (Si/C) composite as anode materials for lithium-ion batteries was synthesized to find the effect of binders and an electrolyte additive. Si/C composites were prepared by two step method, including magnesiothermic reduction of SBA-15 (Santa Barbara Amorphous material No. 15) and carbonization of phenol resin. The electrochemical performances of Si/C composites were investigated by charge/discharge, cyclic voltammetry and impedance tests. The anode electrode of Si/C composite with PAA binder appeared better capacity (1,899 mAh/g) and the capacity retention ratio (92%) than that of other composition coin cells during 40 cycles. Then, Vinylene carbonate (VC) was tested as an electrolyte additive. The influence of this additive on the behavior of Si/C anodes was very positive (3,049 mAh/g), since the VC additive is formed passivation films on Si/C surfaces and suppresses irreversible changes.

• Journal of Dental Rehabilitation and Applied Science
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• v.26 no.3
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• pp.297-309
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• 2010

The objective of the present study was to perform a fracture analysis on fractured implant fixture after use in vivo and make clear the cause & mechanisms of failure. In case of fatigue fracture, the fractured surface represents fatigue striation. Fatigue striation indicate the progression of the crack front under cyclic loading, are characteristic of stage 2 crack growth. The site of crack initiation and stage 1 crack growth were not easily identified in any of the failure, presumably because of the complex microstructural features of the polycrystalline sample. In case of fractured by overload, dimpled or cleavage surface were observed. Using the interpretation of characteristic markings(ratchet mark, fatigue striation, dimple, cleavage et al) in fracture surfaces, failure events containing the crack origin, crack propagation, material deficiency could be understand.

• Transactions of the Korean Society of Mechanical Engineers
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• v.9 no.2
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• pp.140-149
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• 1985

Fully reversed push-pull low cycle fatigue tests under strain control of trapezoid cyclic mode have been conducted in air at temperature of 550.deg. C and with frequency of 0.5 cpm on the domestic stainless steel STS 316 after solution treatment for 1 hour at 1100.deg. C. As an experimental equipment for high temperature fatigue tests, an electric servo-hydraulic fatigue machine(Instron model 1350) was used. This paper presents the effects of creep hold time and plastic strain range on push-pull high temperature low cycle fatigue life and fracture behavior. The fracture surfaces were observed by means of the scanning electron microscope. The results are as follows. (1) The fatigue life decreases with increase of the plastic strain range equal hold time and also decreases as the hold time is getting longer. (2) The frequency modified damage function can predict fatigue life by incorporating a variation of Coffin's frequency modified approach into damage function. (3) The ratios of creep damage and fatigue damage can be calculated by using he linear accumulation damage concept and the ratio of creep damage increases as the hold time is getting longer. (4) At the creep hold time of 5 minutes and the strain range of 2.0%, the fracture mode was intergranular fracture and striations were hardly observed. In this case, the intergranular cracking was originated in void type('.gamma.' type) cracking.

• Steel and Composite Structures
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• v.20 no.5
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• pp.1067-1085
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• 2016

Recent research on steel moment-resisting connection between steel beams and concrete filled steel tubes has shown that there are considerable advantages to be obtained by anchoring the connection to the concrete infill within the tube using anchors in blind bolts. In the research reported here, extensive experimental tests and numerical analyses have been performed to study the anchorage behaviour of cogged deformed reinforcing bars within concrete filled circular steel tubes. This data in essential knowledge for the design of the steel connections that use anchored blind bolts, both for strength and stiffness. A series of pull-out tests were conducted using steel tubes with different diameter to thickness ratios under monotonic and cyclic loading. Both hoop strains and longitudinal strains in the tubes were measured together with applied load and slip. Various lead-in lengths before the bend and length of tailed extension after the bend were examined. These dimensions were limited by the dimensions of the steel tube and did not meet the requirements for "standard" cogs as specified in concrete standards such as AS 3600 and ACI 318. Nevertheless, all of the tested specimens failed by bar fracture outside the steel tubes. A comprehensive 3D Finite Element model was developed to simulate the pull-out tests. The FE model took into account material nonlinearities, deformations in reinforcing bars and interactions between different surfaces. The FE results were found to be in good agreement with experimental results. This model was then used to conduct parametric studies to investigate the influence of the confinement provided by the steel tube on the infilled concrete.

• Journal of the Korean Chemical Society
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• v.24 no.4
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• pp.295-301
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• 1980

The electrical conductivity of solid electrolyte $RbAg_4I_5$ single crystal was studied at various temperatures. The four-probe method was used in measuring the conductance with an ac signal imposed on the specimen. The ionic conductivity was $0.284 ohm^{-1} cm^{-1}\;at\;25^{\circ}C$, and the activation energy for $Ag^+$ ion migration was calulated to be 1.70 kcal/mole. These values agree well with those reported for polycrystalline samples. Reactions at $Ag/RbAg_4I_5$ interface were studied by cyclic voltammetry with a silver reference electrode. It was found that silver ion is reversibly reduced at silver surfaces below zero volt, and iodide was oxidized above +0.67 volt.The anodic current arising from the oxidation of the electrode was small in magnitude initially over a wide range of potential, but, after silver was cathodically deposited on the electrode, reversing the potential sweep to the anodic direction resulted in a sharp peak of anodic current.

• Proceedings of the Korean Society for Rock Mechanics Conference
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• 2000.09a
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• pp.117-128
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• 2000

The development of proper joint model, which can describe real phenomena exactly and still can be used easily, is one of the most important element for the analysis of the mechanical and hydraulic behavior of discontinuous rock mass. In this study, an elasto-plastic constitutive model of joint behavior considering asperity degradation was extended with the concept of first and second order asperities. The proposed model was implemented to numerical code with discrete finite joint element. The parametric study with the various asperity angles and degradation coefficients showed that the model can reproduce the shear behavior of typical rough joints well. Results of laboratory monotonic and cyclic shear tests were compared with those of numerical tests to validate the model. The hydraulic model considering the relations between gouge production and aperture was introduced to the mechanical model. In an attempt to examine the performance of the model, comparative numerical test was conducted. Permeability between joint surfaces increased rapidly at the first stage, but became nearly constant with increasing shear displacement due to gouge production and uniform variation of aperture distribution.